The air-oil tank of an air-oil system exemplifies the type of receptacle to which this invention relates. In an air-oil system, pressure air is fed to a booster by which a relatively large volume of air at a given pressure is applied to the displacement of a smaller volume of hydraulic fluid at a substantially higher pressure. The booster comprises a cylinder and piston mechanism, wherein the air acts on the piston, which moves in a larger-diameter chamber and which has a smaller-diameter rod that is slidable with a close fit in a hydraulic chamber. As the piston is advanced by the pressure air, its rod forces hydraulic fluid out of the hydraulic chamber and into a hydraulic ram. Although the ram may have a rather short stroke, and it is therefore not capable of performing much work, it is capable of exerting a very high force and is thus well adapted for clamping a workpiece and for similar operations where a high force must be exerted and maintained.
An air-oil tank is connected in such a system to provide a source of hydraulic fluid which compensates for any loss of fluid in the hydraulic system. Since the air-oil tank contains pressure air in direct contact with hydraulic fluid, it can provide a source of relatively low pressure hydraulic fluid that can be fed to the ram for returning it to its starting position. The air-oil tank can also serve as an outlet for any air that may have become entrapped in the hydraulic system.
Having in mind that the hydraulic fluid in an air-oil system is subject to very high pressures--which can be on the order of several thousands of pounds per square inch--it will be apparent that for precise and dependable operation of the system the hydraulic fluid that flows out of the air-oil tank must be unmixed with air. Heretofore it has been difficult to satisfy this important requirement in cases where hydraulic fluid was forced into the air-oil tank at any substantially high flow rate, because the liquid then entered the tank in extremely turbulent flow so that it presented a roily surface to air in the tank, mixed with the air, and was thus converted to foam.
Reducing the rate of flow of liquid into the air-oil tank to a value at which foam generation is avoided is impracticable in many installations because pressures and flow rates are fixed by operating requirements and system components and parameters. Usually, baffle arrangements are installed in air-oil tanks to minimize turbulence and churning of incoming liquid, but prior baffles for this purpose have not been fully satisfactory. Those that were reasonably effective in preventing foam generation offered substantial resistance of flow of liquid both into and out of the air-oil tank and thus produced objectionable energy losses and pressure losses that reduced the speed of operation of the system and the forces that could be produced with it.